Carrier aggregation allows a UE to simultaneously receive or transmit on one or more component carriers (CCs). In carrier aggregation, a primary cell (PCell) or another scheduling cell may schedule a UE to listen to the physical downlink shared channel (PDSCH) of a scheduled secondary cell (SCell). The scheduling is done through the use of a physical downlink control channel (PDCCH) at the primary cell or another scheduling cell. Examples of such carrier aggregation are, for example, defined by the Third Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LTE-A) Technical Specification (TS) 36.300, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2”, v.11.3.0, Sep. 26, 2012, the contents of which are incorporated herein by reference.
With carrier aggregation, a UE may need to monitor the PDCCH on the primary cell or another scheduling cell to determine if the UE should receive and decode the PDSCH of the scheduled secondary cell. However, due to the potential PDCCH decoding latency on deciding whether or not there is any scheduling information for any other CCs being scheduled, the radio, as well as other partial baseband processing (channel estimation, time/frequency tracking loops, transmit fast Fourier transform (FFT), among others) might need to be turned on early in order to capture data samples from the scheduled secondary cell. Such capture could be from the PDSCH start time instant at the component carrier, to the time instant that the PDCCH decoding for the scheduled CC is complete. Specifically, the UE may need to buffer the data on the component carriers until it has decoded the PDCCH to ensure that no downlink data carried by the PDSCH is missed while the PDCCHs are decoded.
The added battery usage to have a radio turned on to a component carrier frequency and to buffer the data causes battery drain on the UE.